Firefighters have deployed ground crews to battle a raging southern California wildfire that has nearly tripled in size as it threatened nearly 4,000 homes.

Cooler temperatures and higher humidity were helping efforts against the fire, and firefighters said on Saturday they had contained 30 percent of the blaze, which erupted on Thursday near Malibu, 65km west of Los Angeles.

Light rain forecast for Sunday and heavier precipitation expected for Monday and Tuesday also could help firefighters battling what authorities are calling the Springs Fire.

The Springs Fire grew to 11,330 hectares from 4,040 hectares on Friday morning.

Aerial operations resumed at daybreak after stopping overnight, the Ventura County Fire Department (VCFD) said on its Facebook page, adding that ground crews had continued battling the blaze without interruption.

About 1,900 firefighters had gathered to battle the wind-fanned flames that have ripped through tinder-dry brush, the VCFD said, a nearly two-fold increase in personnel from Friday.

The department said the inferno threatened 4,000 homes, but by Saturday morning, just 15 homes had been damaged and none destroyed.

California typically has fires later in the year, but strong winds and temperatures in the 90s (30s Celsius) have triggered a series of brushfires this week - including a new one in Glendale, just outside Los Angeles.

Evacuations ordered

The fire forced the closure of an eight-mile section of the Pacific Coast Highway (PCH) and a university campus, and reaching a US Navy facility on the coast, reports said.

The VCFD said the PCH had been reopened, but several other roads were closed. Evacuations were ordered over an expanded area on Friday, after winds did an about-turn and pushed the fire back north.

Eight helicopters and six planes were dropping water and fire retardant onto blazing hillsides to protect homes in the area.

"There are some big beautiful homes up there ... But so far, they're doing a good job of protecting them," VCFD spokeswoman Lori Ross told the Los Angeles Times newspaper.

California State University at Channel Islands remained closed, after cancelling all classes and activities at its Camarillo site on Thursday "due to the (fire) and heavy smoke drifting onto the campus".

Wildfires are common across the western United States in the summer, and in southern California they are often fanned by strong offshore Santa Ana winds later in the year, in the fall or winter.

But another blaze erupted on Friday in Glendale, a residential suburb just 13km north of Los Angeles, burning some 75 acres of brush and forcing some local evacuations and the closure a nearby freeway.